A traditional technique of detecting moisture contained in a predetermined region of the ground has been known. For example, a device has been disclosed that detects a water vein through change in distance among and position of four electrodes in dipole-dipole configuration by selection therefrom using a switch (see Patent Literature 1).
Patent Literature 1 discloses a water vein detecting device including a plurality of current electrode pairs, a plurality of potential electrode pairs, a first calculation means, a second calculation means, and an estimation means. The plurality of current electrode pairs each measure a current of an alternating current input to a predetermined region of the ground. The plurality of potential electrode pairs each measure a voltage corresponding to the alternating current. The first calculation means calculates a first resistivity value indicating a resistivity in the predetermined region of the ground using a current and a voltage based on an alternating current having a first frequency. The second calculation means calculates a second resistivity value indicating a resistivity in the predetermined region of the ground using a current and a voltage based on an alternating current having a second frequency higher than the first frequency. When the second resistivity value is larger than the first resistivity value and a difference therebetween is at least a specific value, the estimation means estimates that the predetermined region of the ground includes a water vein.
It is also disclosed that the above water vein detecting device detects a water vein in the same region of the ground based on two types of resistivity values obtained from the alternating currents having the different two frequencies, thereby enabling achievement of highly accurate detection of a water vein.